Understanding youth and young adult cannabis use in Canada post-legalization: a scoping review on a public health issue

Background Canada legalized recreational cannabis in 2018, and one of the primary objectives of the Cannabis Act was to protect youth by reducing their access to cannabis and providing public education. Canada has the highest prevalence of cannabis use worldwide, particularly among youth and young adults under the age of 25. Cannabis use is linked with many adverse effects for youth and young adults including psychosis, anxiety, depression, respiratory distress, cannabinoid hyperemesis syndrome, and impaired cognitive performance. Despite the high prevalence of cannabis use and the evolution of policies in Canada and globally, significant knowledge and research gaps remain regarding youth and young adult cannabis use. The aim of this scoping review is to map the extent, nature, and range of evidence available on youth and young adult cannabis use in Canada since its legalization, in order to strengthen policies, services, treatments, training, and public education strategies. Methods Using a scoping review framework developed by Arksey and O’Malley, along with the PRISMA-ScR guidelines, we conducted a rigorous search in five academic databases: MEDLINE, Embase, APA PsycINFO, CINAHL and Web of Science Core Collection. We included empirical studies that collected data in Canada after the legalization of recreational cannabis (October 2018) and focused on youth or young adults < 30. Two reviewers independently screened articles in two stages and extracted relevant information from articles meeting the inclusion criteria. Results Of the 47 articles meeting our inclusion criteria, 92% used quantitative methods, 6% were qualitative, and 2% used a mixed-methods approach. Over two-thirds (68%) used secondary data. These studies were categorized into six focus areas: (1) prevalence, patterns, and trends, (2) cannabis-related injuries and emergency department (ED) visits, (3) rates and patterns during the pandemic, (4) perceptions of cannabis use, (5) prevention tools, and (6) cannabis-related offenses. Key findings from the studies reviewed include an increase in cannabis use among 18-24-year-olds post-legalization, with mixed results for youth under 18. ED visits for intentional and unintentional cannabis-related injuries have increased in young children and teens. Perception studies show a mix of concern and normalization of cannabis use. Though limited, prevention studies are promising in raising awareness. A decline in cannabis-related offenses was noted by one study. The review highlights several research gaps, including the need for more qualitative data, disaggregation of demographic data, intervention research, and comprehensive studies on the physical and mental health impacts of cannabis use among youth and young adults. Conclusion Maintaining a public health approach is critical, with a focus on reducing the high prevalence of cannabis use among youth and young adults. This involves implementing prevention strategies to minimize harms, enhancing public education, minimizing commercialization, reducing youth access to cannabis, promoting guidelines for lower-risk cannabis use and harm reduction strategies, and increasing training for healthcare providers. Supplementary Information The online version contains supplementary material available at 10.1186/s13011-024-00615-9.


Introduction
Canada ranks among the top countries globally for cannabis use prevalence [1].According to the Canadian Cannabis Survey (CCS), the highest usage rates are in young adults aged 20-24, with 51% reporting past-year use.This is followed by 37% of those aged 16-19, compared to 21% of adults over the age of 25 [2].Daily cannabis use, which is linked to more significant adverse effects, is reported by 16% of 16-19-year-olds and 23% of those aged 20 to 24 [2].The CCS also indicates that 66% of bisexual and 58.3% of gay or lesbian young adults reported past-month use, compared to 45% of heterosexual young adults.In terms of racial identity, youth and young adults who identify as white have the highest rates of cannabis use [2].
Canada legalized recreational cannabis in 2018, with the nationwide policy aiming to regulate the sale and distribution of cannabis.One of the primary objectives of the Cannabis Act was to protect public health and safety, particularly focusing on protecting young people by reducing incentives to use cannabis and restricting access [3].However, since legalization, 45.5% of those aged 16-19 and 49.8% of 20-24-year-olds have reported increased cannabis consumption [2].Furthermore, youth and young adults have reported easier access to cannabis since its legalization [4,5].Notably, 41% of students in grades 7-12 in Ontario -Canada's most populous province, reported easy access to cannabis in the Ontario Student Drug and Health Survey (OSDHUS) [6].
A significant proportion of youth and young adults use cannabis products with tetrahydrocannabinol (THC) levels over 20%, a stark increase from the 3% levels seen in the 1980s [2].THC is the main psychoactive ingredient in cannabis, and higher potencies are more harmful, especially for young people.In a position paper written pre-legalization and reaffirmed in 2023, the Canadian Paediatric Society (CPS) recommended limiting THC concentration in legally purchased cannabis for young adults aged 18-25.The CPS explains that there are higher risks associated with cannabis use during this important developmental period, as the brains of young adults have not fully developed [25].
The data show a correlation between young people's self-reports of their mental health and their cannabis use.For example, among 16-19-year-olds, 44.9% of those who rated their mental health as poor reported using cannabis in the past 12 months, compared to 24.4% of those who rated their mental health as excellent.Similarly, in the 20-24-year-old group, 34.5% who considered their mental health excellent used cannabis, but this ratenearly doubled to 67.3% among those who perceived their mental health as poor [2].A systematic review and meta-analysis by Leung et al. [26] found that 22% of individuals who use cannabis have cannabis use disorder, 13% abuse cannabis, and another 13% have cannabis dependence, with higher risks in young people and those who are using weekly or daily.
Despite the widespread use of cannabis and evolving policies in Canada and around the world, significant knowledge and research gaps persist regarding cannabis use among youth and young adults in Canada since legalization [27].A number of systematic and scoping reviews have examined cannabis use and legalization, though they are not specifically focused on Canada [28][29][30][31][32] or not focused on youth and young adult populations since legalization [26,33,34].Among those reviews focusing on youth or young adults, most are not specific to Canada and concentrate on specific areas such as driving [35], cognitive functioning [36], co-occurring cannabis use with other substances or behaviours [37], and psychosocial interventions for cannabis reduction in young adults with psychosis [38].Rubin-Kahana and colleagues [39] explored the impact of cannabis legalization on youth in Canada, but this was a narrative review that did not adhere to systematic or scoping review guidelines and did not have a list of studies selected for the review.To our knowledge, there are no systematic or scoping reviews that have been conducted since cannabis legalization in Canada that focus specifically on youth and young adults.This type of review is relevant and necessary especially at this early stage of legalization while the government assesses the public health effects, particularly the impact on youth and young adults [33,39,40].
A public health approach to the regulation of cannabis has been recognized as an important strategy that focuses on minimizing harms and promoting health [33,41].It is an evidence-based approach, relying on the best available scientific evidence to inform policy and practice decisions [40,41].To address some of the gaps identified in the literature, this scoping review aims to map the extent, nature, and range of evidence available on youth and young adult cannabis use in Canada post-legalization to strengthen policies, services, treatments, training, and public education strategies.Our review focused on the following research questions: (1) What types of literature are available that describe youth and young adult cannabis use in Canada since its legalization?(2) What evidence does the literature provide regarding youth and young adult cannabis use following its legalization in Canada?(3) What are the identified limitations, gaps, and recommendations in the literature concerning youth and young adult cannabis use since its legalization?

Methods
This scoping review followed the framework established by Arksey and O'Malley [42], which comprises five key stages: (1) defining research questions, (2) identifying relevant articles, (3) selecting and incorporating pertinent material, (4) charting data, and (5) synthesizing and reporting the findings.In the final phase, the authors conducted a narrative synthesis of the results, presenting them through written summaries and descriptive charts.A narrative synthesis identifies patterns, similarities, and differences across studies [42], allowing the authors to organize the literature thematically in different categories.Scoping reviews primarily aim to synthesize and map existing literature related to a specific research topic, without focusing on appraising the methodological rigor of the selected material [43].The rationale, objectives, and methods of this scoping review were detailed in a peer-reviewed scoping review protocol to enhance methodological transparency [44].We adhered to the standards outlined in the PRISMA Extension for Scoping Reviews (PRISMA-ScR) checklist [45], which is available as a supplemental document (Appendix A).

Identifying relevant articles
A member of the research team who is a social sciences librarian (JL) designed a comprehensive search of the published literature.Text words and controlled vocabulary relating to youth, cannabis, and Canada were adapted from reputable published search strings [46][47][48][49].A pilot search strategy, developed for Medline (Ovid), underwent peer review by an independent librarian using the Peer Review of Electronic Search Strategies (PRESS) framework [50].This pilot strategy was then translated into Embase (Ovid), APA PsycINFO (Ovid), CINAHL (EBSCO), and Web of Science Core Collection, which includes Science Citation Index Expanded, Social Sciences Citation Index, Arts & Humanities Citation Index, Emerging Sources Citation Index, Conference Proceedings Citation Index, and Book Citation Index.Search results were downloaded on December 8, 2021, and uploaded to Covidence for deduplication and screening.The search was rerun on July 14, 2022, and March 8, 2023, to capture articles published or added to the databases since the initial download, yielding 149 and 229 studies for screening, respectively.A date limit of the year 2000 + was applied to all searches.After the first update on July 14, 2022, we revised the inclusion criteria to exclude results published before the legalization of cannabis in Canada in 2018.However, we decided not to change the publication date limit in the next update on March 8, 2023, opting instead to manually screen out studies published between 2000 and October 2018 that had not already been excluded.The full search strategy in five databases is available as a supplemental document (Appendix B).

Article selection and inclusion
Articles were eligible for inclusion in this study if they (1) were written in English or French, (2) were empirical studies published in peer-reviewed journals, (3) focused on recreational cannabis use in youth and young adults aged 29 and younger, 4) were conducted in Canada, 5) collected data post-legalization of recreational cannabis on October 17, 2018.The most recent search we conducted was in March 2023, and we included articles up to that point.We excluded gray literature, dissertations, editorials, commentaries, books, book chapters, book reviews, interviews, newspapers, conference abstracts, and reviews.Articles with participants aged 30 and over were included if there was also a subsample of youth or young adults under the age of 30.Throughout this review, the term "youth" refers to anyone under the age of 18 and "young adult" refers to anyone under the age of 30.The Cannabis Act refers specifically to "young persons" as those under the age of 18 [3].However, Health Canada [41], the Canadian Paediatric Society [25], the Mental Health Commission of Canada (MHCC) [51], and many researchers have discussed concerns about cannabis use in young adults aged 18-24, a group with the highest prevalence of cannabis use and who are in a period of continued brain development.For this scoping review, we included up to age 29 aligning with the MHCC which states that this stage of development can extend up to age 30 [51].Our aim was to ensure we do not miss research studies due to a narrow age range for young adults and a preliminary literature scan showed that some studies had young adult samples up to age 25, while others went up to age 29.
Articles focused on substances other than cannabis or on polysubstance use were excluded, unless cannabis was specifically mentioned as one of the substances of interest in the abstract.Articles on the medical use of cannabis, as well as those that did not collect data in Canada, were excluded.However, studies collecting data from multiple countries were included if Canadian data were separately analyzed and reported.Trained members of our research team (RV, TE, AK, SM, TK) applied these inclusion and exclusion criteria and screened the articles in two stages.The first stage involved screening by title and abstract, while the second stage entailed a full-text review of articles that met inclusion criteria in the first stage.

Charting data
The subsequent stage of the review involved charting and extracting data from articles that met inclusion criteria.The charting categories were aligned with our research questions and included: (1) author(s), (2) title, (3) year, (4) language, (5) province/territory, (6) journal, (7) aim of study, (8) research method, (9) research design, (10) sample size and characteristics, (11) key findings related to cannabis, (12) gaps or limitations, and (13) recommendations.This phase followed an iterative approach.Four members of the research team (TK, RV, SM, AK) conducted a comprehensive review of all selected articles, utilizing a charting template to synthesize and analyze the key findings from these articles [52].
Most studies employed quantitative research methods (n = 43, 92%), with only three studies (6%) utilizing qualitative methods [73,91,94], and one (2%) using a mixed method approach [80].Over two thirds of the studies (n = 32, 68.09%) used secondary data from various sources, with the most frequently cited being the COM-PASS study (n = 9, 19.15%) which is a longitudinal study following Canadian high school students.

Categories by areas of study focus
In our review, we grouped the 47 studies into six categories based on their focus areas.The first category, with the highest number of studies (n = 17), examined the prevalence, patterns, trends, and characteristics of cannabis use among youth and young adults.This category is further divided into two subgroups: the first, with seven studies, focused on changes in cannabis use rates postlegalization [4,15,56,60,69,76,88] and the second subgroup, comprising ten studies, on patterns, trends, and characteristics of cannabis use in youth and young adults since legalization [63,65,67,68,70,75,79,85,92,95].
The second category encompassed twelve studies examining cannabis-related injuries and emergency department (ED) visits attributable to cannabis [53,62,64,72,74,77,81,83,84,86,87,93].While most studies in this category examined the rates of ED visits since legalization, two examined trends related to vaping [53,62], and one study examined traffic injury presentations related to cannabis in EDs [72].It is important to note that although two studies examined hospital visits during the COVID-19 pandemic [81,86], we grouped them with the ED visits, rather than the COVID-19 category because the primary focus was ED visits and cannabisrelated injuries.
The third category, consisting of nine studies, specifically focused on cannabis use rates and patterns during the COVID-19 pandemic [17,20,58,59,61,66,71,78,89].The fourth category, includes nine articles exploring Fig. 1 PRISMA flowchart of the search and screening process perceptions related to cannabis use: four focus on youth and young adult perceptions post-legalization [57,73,90,94] one examines perceptions of substance use services [91] and another explores perceptions of cannabis policies and penalties related to immigrants and prejudices [54].
The fifth category consists of two articles focused on prevention tools.The first is aimed at preventing cannabis-impaired driving [82], and the second focuses on increasing awareness among Black youth and young adults about cannabis and psychosis through a psychoeducational video game [80].Finally, the sixth category consists of a single article that focuses on cannabis-related offences since legalization [55].For a full list of selected articles and a synthesis of results, see Table 2.

Findings of selected studies
Category 1: Prevalence, patterns, trends and characteristics (n = 17): Among the seven studies examining cannabis use rates, 71.42% found that the prevalence has increased post-legalization, especially among young adults aged 18-24 [4,15,56,69,76].For example, Fischer et al. [56] examined data from three surveys and found that rates were highest among young adults in all three surveys, with significant increases after legalization.The study also found that 40% of respondents under the legal age reported it was very easy to access cannabis.Another study by Vignault et al. [15] found increased use of cannabis and an increase in the diagnosis of cannabis use disorder, with more significant increases in young adults aged 18-24.Hammond et al. [76]  The study found that greater interaction with immigrants among undergraduate participants was linked to lower support for harsh cannabis-related penalties for immigrants.High-quality contact with immigrants was associated with stronger opposition to such penalties.Furthermore, individuals with right-wing ideologies tended to support more severe penalties for outgroup members (immigrants) compared to ingroup members (Canadians in general).Participants perceived an overall increase in cannabis use post-legalization, a reduction in stigma, and a normalization of cannabis in everyday life.The study found a tendency for risk denial among participants.They were aware of some of the risks associated with cannabis use but did not believe these risks applied to their own health.Additionally, they viewed cannabis as healthier than prescription medications.The most commonly acknowledged physical health risk was lung injury.Many participants reported using cannabis to manage mental and physical health issues, including anxiety, sleep problems, stress, and bipolar disorder.that the prevalence of ever use were significantly higher the year following legalization, but rates of regular use stayed the same.The study also found provincial differences with lower rates in Québec and British Columbia.In contrast, Gueye et al. [88] found that cannabis use levels only increased for young adults aged 18-24 who were using regularly, defined as three times or more in the past month.Nguyen & Mital [4] examined changes in cannabis use among youth and young adults aged 15-20 in Québec before and after the province increased the minimum legal age (MLA) for cannabis use from 18 to 21 years.The study found that the MLA change was not associated with changes in cannabis use among youth aged 15 to 17. However there was an increase in cannabis use among those aged 18 to 20.Notably, this increase was 51% lower in Québec compared to other provinces, a difference that was attributed to the increase in the MLA.Contrary to the other studies in the subgroup examining prevalence rates, the study by Nguyen et al. [60], which focused on cannabis use in 15-18-year-olds, did not find a significant increase in prevalence rates.However, it did report increases in the initiation of cannabis use among never users and easier access to cannabis.
Among the ten studies examining patterns and trends in youth and young adult cannabis use, several findings stand out as particularly noteworthy.Firstly, only a few studies examined or found gender differences in patterns or modes of use [65,67,75].Hammond et al. [75] and Williams et al. [67] found a higher likelihood of daily or weekly cannabis use among males, while Romano, Butler et al. [65] did not find a significant gender difference in risky cannabis use behaviours and mode of use.An increase in multimodal cannabis use was another trend identified by some studies [65,70,75], although smoking remains the most common mode of use [65].Studies found that multiple modes of cannabis use were associated with higher frequency of use and solitary use [65,79], as well as depressive symptoms [70].Hammond et al. [75] found that the standard size of a joint increased from 0.2 g in 2018 to 1.0 g in 2020.Three studies found that polysubstance use was pervasive among youth and young adults [67,68,79].Yang et al. [68] identified four distinct polysubstance use patterns in middle and high school students: (1) no use, (2) single use of alcohol, (3) dual use of cigarettes and alcohol, and (4) multi-use.They found that youth are more likely to remain in the same subgroup of use pattern or transition to a higher use group as they age.The study also showed that cannabis use rates were four times higher in 2018-19 than they were in 2016-17.Williams et al. [67] found that consistent polysubstance use was associated with depression in high school students.
Two studies examined youth cannabis use rates and school approaches [63,95].Butler et al. [95] found no significant changes in school priorities pre-and postlegalization.Substance use was not a leading priority, and school prioritization of cannabis use was not associated with student cannabis behaviours.Magier et al. [63] found that school disciplinary approaches were not associated with cannabis use, but they were associated with student perceptions.Students who perceived their school to be more unsupportive reported higher rates of cannabis use.Finally, a study by Hammami & Katapally [92] with a sample of 818 youth found that cannabis use was a risk factor associated with a higher suicide ideation risk for youth aged 13-18.
Category 2: Cannabis-related injuries and ED visits (n = 12): Most studies in the second category showed an  increase in ED visits since legalization [64,74,77,81,83,84,86,87,93] with two focused on unintentional cannabis-related injuries or poisonings [64,77], one on intentional injuries [74], and the remaining studies reporting on both unintentional and intentional cannabis-related injuries [81,83,84,86,87,93].One study on unintentional exposures found that 76% of accidental exposures were attributed to edible products [77].Another study compared unintentional exposures in the pre-legalization and post-legalization data.They found that of the 581 hospitalizations for cannabis poisoning, 20.65% were prelegalization and 79.35% occurred post-legalization [64].An Alberta study also found an increase in unintentional ingestions in children 0-11, as well as adolescents aged 15-17 [93].A Québec study found increases in hospitalizations post-legalization among boys aged 10-14 years, with 70% of substance-related hospitalizations after legalization involving cannabis, compared with 39.3% pre-legalization [87].Kim et al. [81] studied ED visits in Ontario and found that cannabis-related visits increased in 2020 compared to 2019 among young adults 18-25 years more than among youth 10-17 years.Additionally, young adults with cannabis-related ED visits had triage to end times longer than six hours with higher rates of emergent or life threatening triage levels.Another Ontario study found that there was an increase in cannabis poisonings due to recreational use among 16-18-yearolds.The proportion of cannabis cases increased from 28% in 2018 to 40.4% in 2020 among those aged 16-18, with no significant changes in poisonings from other substances including alcohol, opioids, acetaminaphen, and prescription medications [86].
Three studies reported on increased cases of cannabinoid hyperemesis syndrome (CHS) post-legalization, a condition more commonly observed in individuals with cannabis use disorder or those who use cannabis chronically [74,84,93].Andrews et al. [74] found that the treatment prevalence for CHS doubled between 2017 and 2021 among youth and young adults aged 16-24 in Alberta and also reported that youth and young adults with CHS had high rates of co-occurring anxiety and depression.
Two studies examined vaping-related injuries (VAPI), with one focused on VAPI patients aged 15 to 50+ [53] and the other examining VAPI cases aged 17 years and younger [62].Zutrauen et al. [62] found that that 68% of patients were 15-17 years old and nicotine vaping was responsible for 42% of injuries, with cannabis accounting for 24% of vaping-related injuries.Baker et al. [53] reported that 25% of vaping-associated lung illness (VALI) patients were youth and young adults aged 16-19 and 40% report vaping or dabbing cannabis.The authors noted that 80% of VALI patients were hospitalized.Data for young adults aged 20-24 is unavailable because they were categorized with the 25-49 year old age group.
Three studies attributed increased pediatric poisonings, ED visits, and hospitalizations to the commercialization of cannabis [64,83,84].Myran, Pugliese et al. [83] found that there were significant increases in cannabisrelated ED visits, with the most changes in youth and young adults aged 15-24.The authors noted that this coincided with large increases in the number of cannabis stores and sales.All three studies on cannabis-related injuries and commercialization recommend stricter regulations on the number of cannabis dispensaries, the sale of products appealing to youth and young adults such as edibles, and the minimum legal age for purchasing cannabis [64,83,84].One study, differing in focus from others examining ED visits, was by Callaghan, Sanches et al. [72].This study examined traffic-injury ED presentations since the legalization of cannabis and found no significant changes.
Category 3: cannabis use rates and patterns during the COVID-19 pandemic (n = 9): In this category, most studies examining youth and young adult cannabis use rates during the pandemic found that the rates increased, and isolation was associated with increased rates [17,61,78].Three studies examining trends found that the odds of increased cannabis use were higher for those ages 18-29 [58,59] and for youth who were using cannabis to cope with the pandemic [71].A study by Pocuca et al. [20] during the first three months of the pandemic in Québec found that overall there were no changes in cannabis use, but noted that young adults with preexisting vulnerabilities increased their substance use.Another study examining COVID-19 measures and substance use did not find a relationship between adherence to these measures and cannabis use.The study reported that youth using cannabis perceived these measures as less strict, which was interpreted to be related to the perception that alcohol use is more social, while cannabis use is more solitary [66].Salmon et al. [89] examined characteristics and trends of cannabis use in youth and young adults with adverse childhood experiences (ACEs) during the COVID-19 pandemic.The study found that youth and young adults with a history of ACEs experienced increased pandemic-related stressors and showed increased use of alcohol and cannabis.
Category 4: Perceptions related to cannabis use (n = 6): Robinson et al. [90] examined the differences in perceptions of grade 8 students regarding the legalization of cannabis, both pre-and post-legalization.The study found that adolescents generally held negative views toward cannabis legalization, and these perspectives did not change post-legalization.Harris-Lane et al. [57] found that young adults aged 18-25 years tend to minimize their cannabis use and are more adept at perceiving risks in young adolescents than in themselves.In a similar vein, MacDougall & Maston [73] observed that undergraduates in their study reported an overall reduction in stigma post-legalization, and a normalization of cannabis in everyday life.The authors noted a "risk denial" among participants who described cannabis as healthier than prescription medication and used it to manage physical and mental health problems.Another study conducted in Newfoundland & Labrador indicated that youth and young adults do not believe that they receive adequate education about cannabis across the province and expressed a need for more evidence-informed cannabis education through media and schools [Bishop et al., 2022].Turuba et al. [91] explored how youth and young adults perceive substance use services in British Columbia.Participants highlighted that cannabis use is often overlooked by service providers, noting a lack of recognition that cannabis is an addictive substance.They emphasized the need for more information about addictions and noted that there are challenges in accessing substance use services.The final study in this category examined perceptions of cannabis-related penalties for immigrants and found that right-wing ideology was associated with more support for harsher penalties for immigrants than non-immigrants [54].
Category 5: Prevention tools for youth and young adults (n = 2): Jani et al. [80] evaluated an online psychoeducational program for Black youth and young adults on cannabis and psychosis with nine participants aged 16-19.Participants showed increased awareness after playing the psychoeducational video game, which was supplemented with a tutorial intervention [80].The second study examined how a digital tool can provide information about responsible cannabis use and prevent cannabis-impaired driving.The study found that 73.6% of youth and young adult respondents used cannabis, with 30.8% reporting that they drove after cannabis use.Additionally, gender was not found to be a significant determinant of driving after cannabis use [82].
Category 6: Cannabis-related offences (n = 1): There was only one study in this category, which examined police-reported cannabis-related crime among youth aged 12-17 [55].The study found decreases in cannabisrelated crimes among male and female youth in this age group.This finding followed a decreasing trend in police reported cannabis-related incidents pre-legalization, attributed to normalization and decriminalization.The study reported a 65% decrease in cannabis-related crimes for females and 55% decrease among males over 76 days post-legalization.However, the study was limited to a short-term period and did not disaggregate the data by race or ethnicity, which is necessary to determine if the decreases occurred among populations historically overrepresented in the criminal justice system.

Discussion
In this scoping review, we identified and synthesized 47 studies that examined youth and young adult cannabis use in Canada since its legalization.The review aimed to examine the extent, nature, and range of available evidence on this topic to inform and enhance policies, services, and public education strategies.Several key findings emerged from the review.First, regarding prevalence, most studies indicated an increase in cannabis use and cannabis use disorders among young adults aged 18-24 since legalization.During the pandemic, higher rates of use were reported, particularly among young adults aged 18-29 years and those who had never used cannabis before the pandemic.For youth under 18, the results were mixed: some studies reported increased overall rates, others found no significant changes, and a few noted earlier initiation rates.There was also an increased likelihood of higher usage rates among youth post-legalization, especially in those who had already been using cannabis frequently before legalization.In terms of trends, the studies showed that smoking is the most common mode of use, but multimodal and polysubstance use are increasingly observed among youth and young adults.Most studies that examined ED visits and hospitalizations due to cannabis-related injuries reported an increase in visits for both intentional and unintentional poisonings in young children and teens.
Since legalization, the increased prevalence of cannabis use among youth and young adults, as well as the increase in cannabis-related injuries and emergency department visits, can be attributed to several interconnected factors.Notably, the enhanced availability and accessibility of cannabis is a contributing factor.Manthey et al. [30] conducted a systematic review on the impact of legal cannabis availability and found that higher availability was associated with an increased likelihood of cannabis use.The review also identified a link between the number of cannabis retail stores and youth cannabis use, despite legal age restrictions on cannabis purchases.The authors offer several explanations for this trend, including the lack of strict enforcement of age restrictions at cannabis outlets and youths' access to cannabis through family and friends.Furthermore, they suggest that high availability and less restrictive regulatory measures contribute to the normalization of cannabis use, leading to higher rates of experimentation and increased demand.This explanation has been supported by studies on trends in Oregon [96] and Uruguay [97] which showed that youth found it easier to obtain cannabis post-legalization.Enforcing age restrictions may have some challenges in Canada, with 38.2% of young people aged 16-19 reporting that they have purchased cannabis from a legal storefront and 3.9% from a legal online store [2].
Research suggests that the commercialization of cannabis plays a role in its high prevalence of use among youth and young adults [34].Myran et al. [34] conducted a scoping review on the health harms associated with cannabis commercialization and reported mixed results, with five studies out of 14 indicating increases in health harms post-legalization.The authors explain that these mixed findings are related to the level of market maturity, noting that most studies focused on changes within the year following legalization.They argue that cannabisrelated harms may be more accurately assessed as the market (e.g., the expansion of retail stores) and products (e.g., those with higher THC levels) grow.One of the studies selected for this review observed higher rates of cannabis-related hospitalizations in three provinces (Ontario, Alberta, British Columbia) that allow the sale of edibles, in contrast to Québec, which prohibits the sale of edibles appealing to children, including sweets, desserts, chocolates and candies.During the examined period, rates of cannabis-related hospitalizations more than doubled in the three provinces that permitted the sale of commercial edibles, while in Québec the rate of hospitalizations remained unchanged [64].
A study examining access to legal cannabis stores since legalization, found a 122.3% increase in per capita stores, with considerable differences between jurisdictions and between public and private retail models.For example, Ontario's private retail model offers extensive access with 1,552 cannabis stores, in contrast to Québec, which has 91 stores under a public model [64] managed by the Société Québécoise du cannabis (SQDC).This public model mandates that most profits be directed to research and prevention strategies [99].
Some studies in our review suggest that the high prevalence of cannabis use among youth and young adults can be partly attributed to decreased perceptions of its risks and harms.This trend of minimizing of risks is also reflected in responses to the Canadian Cannabis Survey, which found that only 14.8% of individuals over 16 who regularly smoke cannabis perceive it as a serious risk, compared to 75.7% of respondents who regularly smoked tobacco in the past 12 months [2].Ali et al. [100] highlight how public discourse influences the initiation and continued use of substances among youth.They discuss the normalization and social acceptability of substances like cannabis, along with increased availability, and how these factors may affect usage among youth and young adults.This study draws on the normalization framework introduced by Parker and colleagues [101], which outlines shifts in cultural attitudes and behaviours resulting in a substance being less stigmatized.Using this framework, Asbridge et al. [102] compared the normalization of cannabis with the denormalization of tobacco.Denormalization refers to the adoption new values and rejection of certain behaviours that were viewed as acceptable or mainstream.In the case of tobacco, policies and educational efforts have played a crucial role in altering social and cultural norms.The study emphasized that perceptions of health risks significantly influence the processes of normalization and denormalization, suggesting that while normalization can reduce stigma, it must be balanced with education on harms and risks [100].
Public awareness of the risks and harms associated with cannabis use among youth and young adults remains relatively low.Enhancing public awareness of these health risks is an objective in the Cannabis Act [3], yet 48% of Canadians report not having noticed any educational campaigns or public health messages about cannabis.Furthermore, 52% have not observed health warning messages on cannabis products, and only 11% of Canadians have noticed public health messages about cannabis in health care settings [2].The Canadian Centre on Substance Use and Addiction (CCSA) [103] conducted a public consultation after five years of cannabis legalization and found persistent misinformation and low cannabis literacy among Canadians.They indicated that this limited understanding of risks and harms suggests Canadians may not be making informed health choices.The CCSA recommended more robust public education efforts, especially aimed at priority groups such as youth.There are also knowledge and skills gaps in service providers, highlighting the need for increased training and education programs focused on youth and young adult cannabis use [104].
The evidence gathered from this scoping review underlines the need to enhance efforts to to protect youth and young adults and minimize risks and harms associated with cannabis legalization.In 2016, the Government of Canada formed a Task Force in preparation for legalization, responsible for developing a framework for the legalization and regulation of cannabis [41].The Task Force highlighted the risks of cannabis use, particularly to children, youth, young adults, and other vulnerable groups.To mitigate these risks, it recommended a public health approach that "delays the age of initiation, reduces the frequency of use, reduces higher-risk use, reduces problematic use and dependence, expands access to treatment and prevention programs, and ensures early and sustained public education and awareness" [41p15].Enphasizing the ongoing brain development in young adults aged 18-25, the Task Force stressed the importance of public health measures to discourage and delay cannabis use, including through advertising restrictions and public education.In 2022, an Expert Panel was formed to conduct a Legislative Review of the Cannabis Act [105].The Expert Panel wrote a report published in March 2024 which emphasized the need for increased efforts to reduce cannabis use in youth and young adults and highlighted the importance of increasing public awareness about the health risks associated with cannabis use through prevention initiatives.The panel agreed with the pre-legalization Task Force, which stated that "revenue generation should be a secondary consideration for all governments, with the protection and promotion of public health and safety as the primary goals" [105p19].
The need to strengthen the public health approach was further emphasized in a recent systematic review that examined how the literature describes and defines a public health approach to substance use [40].The review argued that an effective public health approach in jurisdictions with legalized cannabis should include the best available evidence, a focus on reducing harm by addressing modifiable risk factors, efforts to minimize commercialization, and regulation measures such as availability, marketing, and promotion of cannabis [40].
Our findings identified several gaps in the current research on cannabis use in youth and young adults.First, there is a notable scarcity of qualitative or mixedmethod studies, with a high percentage of research relying on secondary and aggregate data.The scarcity of qualitative data, along with the abundance of secondary data, limits our understanding of how cannabis use affects young people.Additionally, few studies examined the social determinants of health in relation to cannabis use.Despite sexual and gender minority youth (SGMY) in Canada having the highest rates of cannabis use, none of the studies in this review collected data on sexual orientation.Furthermore, many studies did not include racial data, and in instances where race was presented, it was often categorized as white or non-white.Also, the studies frequently presented gender in a binary manner (male or female) or categorized gender as male, female, and other.
Another literature gap is the tendency to group young adults aged 18-24 with the general adult population.There is ample evidence of increased cannabis use among young adults following legalization, suggesting that they should be treated as a distinct group in future studies.Only two studies explored digital prevention programs, and none focused exclusively on cannabis treatments or interventions.Research on the relationship between cannabis use and physical and mental health was also limited.
There was only one study examining the impact of legalization on cannabis-related offenses among youth (12)(13)(14)(15)(16)(17), which showed short-term reductions in criminalization [55].Since this search was conducted, another study was published, examining cannabis-related criminalization among youth and identifying significant reductions in cannabis-related offenses.These findings show important progress in deterring illicit activities, which is also one of the objectives of the Cannabis Act [106].Nonetheless, there is a need for future studies to collect and present disaggregated data by race and ethnicity to determine whether there have been reductions in cannabis-related criminalization among racialized youth who have historically faced unjust and disproportionate persecution for cannabis possession and use [107].

Strengths and limitations
One of the inherent limitations of a scoping review is the lack of quality appraisal of the studies, although this is not its primary objective.Instead, a scoping review aims to map out the literature and provide a broader perspective on the topic.We excluded grey literature due to feasibility issues;, it is harder to locate, often lacks abstracts for screening, and varies widely in quality due to the absence of peer review and journal standards.Another potential limitation of this review is the unintentional omission of relevant studies.We minimized this risk by ensuring our research team includes a librarian with expertise in relevant databases, who was also responsible for developing a robust search strategy.We also conducted three searches to try to capure the most recent literature since the last search.Our scoping review had many strengths including being the first to synthesize studies focused on youth and young adult cannabis use since legalization in Canada.We adhered to the PRISMA-ScR checklist, which increased transparency and reduced bias.Finally, two screeners independently revieweds each article, with a third screener resolving any discrepancies.

Conclusions
Recreational cannabis was legalized in Canada in 2018, raising concerns about its prevalence among youth and young adults, along with the associated risks and harms.Maintaining a public health approach is critical, focusing on reducing the high prevalence of cannabis use among youth and young adults.This involves implementing prevention strategies to minimize harms, enhancing public education, reducing commercialization, limiting youth access to cannabis, promoting guidelines for lower-risk cannabis use, and increasing training for healthcare providers.While this scoping review addressed some gaps in the literature, it also highlights the existence of many remaining knowledge gaps.There is a pressing need for further research to inform policy, practice, education, and training.

Table 1
Characteristics of Selected Studies (N = 47)

Note Many articles were not limited to a single subject area, but they were categorized based on the primary focus of the study Authors & Year Study Location Sample size and population Research Method Category & aim of study Findings
25% of VALI cases involved youths aged 16 to 19.VALI patients reported using cannabis-related vaping or dabbing products.All patients under 20 who reported vaping using both nicotine-and cannabis-containing products, were youth under 20.80% of VALI patients required hospitalized.

Table 2
Full set of selected articles and synthesis of results (N = 47)

Study Location Sample size and population Research Method Category & aim of study Findings
Post-legalization, there were 32 cases of child/youth exposure compared to 5 pre-legalization.Accidental exposures, primarily due to edible products, accounted for 76% of incidents.The most common abnormal vital sign was tachycardia.The most frequent signs and symptoms were altered level of consciousness (76%), lethargy (59%), vomiting (30%), and seizures (22%).